Abstract
In addition to its well-established function in supplying the energy for CO2 assimilation, light plays a regulatory role in photosynthesis. The ferredoxin-thioredoxin system is a major mechanism whereby light functions in this capacity. Here, light absorbed by chlorophyll is converted via ferredoxin into a reductant messenger, reduced thioredoxin, that interacts with key target enzymes, thereby changing their catalytic activities. In this way, the green plant achieves maximum efficiency of its photosynthetic (light) and heterotrophic (dark) capabilities.